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  Material processing system with variable repetition rate laserUSPTO Application #: 20080025351Title: Material processing system with variable repetition rate laser Abstract: A system for using a pulsed laser beam to process materials includes a selector for varying the pulse repetition rate of the laser beam. Also included is a control unit for identifying an optimal pulse repetition rate that is compatible with the required pulse energy level for processing the material. Variations in the pulse repetition rate can be made during a procedure pursuant to either pre-programmed instructions, or in response to closed loop feedback controls. (end of abstract) Agent: Nydegger & Associates - San Diego, CA, US Inventor: Frieder Loesel USPTO Applicaton #: 20080025351 - Class: 372 25 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20080025351. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001]The present invention pertains generally to laser systems that are used to alter and process materials. More particularly, the present invention pertains to pulsed laser systems that are used for processing materials with procedure sections that require different energy levels for laser-material interaction (i.e. ablation). The present invention is particularly, but not exclusively, useful for employing the effective required energy level while optimizing the pulse repetition rate of a laser system during a material processing procedure. BACKGROUND OF THE INVENTION [0002]Any material, regardless whether it is homogeneous or composite, can be processed in any number of different ways. And, depending on the desired results, the procedure that is selected for processing the material can be performed using operational parameters that may need to be changed during the procedure. Of particular interest here are laser systems that process or alter material for purposes of cutting, reshaping or removing portions of the material(s). As is well known, laser processes for doing this typically involve phenomena such as laser induced optical breakdown (LIOB), photodecomposition, or photoablation. [0003]In recent years (i.e. since the invention of the laser in the 1960s) laser systems have been effectively used to alter or process a significant number of different type materials. More recently, it has been recognized that laser beams which have laser pulses of ultra short duration (e.g. picosecond and femtosecond duration) are particularly effective for many applications. Normally, such laser systems are operated at a fixed level of pulse energy, with a fixed pulse repetition rate. Thus, it has been a standard practice to determine the energy level that is required in laser pulses to effectively process a target material(s). A pulse repetition rate that will maintain this energy level is then accepted. If lower energies would be needed of sections of a processing procedure, the output energy of the laser would be simply reduced using well known types of attenuators while maintaining the same pulse repetition rate. This, however, does not consider the fact that changes in a pulse repetition will result in changes in the energy level of the laser pulses in the beam. It happens for many applications that this fact may be advantageously used. [0004]Referring to FIG. 1, the relation of pulse energy and repetition rate in a typical ultra short pulse laser beam is shown. Specifically, FIG. 1 shows that as the repetition rate (R) of pulses in a laser beam is increased, the energy level (E) of the pulses decreases. Stated differently, the energy level in each pulse is dependent on the pulse repetition rate, and they vary inversely. As indicated above, this trend may be used to advantage because many, in fact most, materials are not homogeneous. Thus, such materials (e.g. composites) will have different energy thresholds for ablation, and therefore require different energy levels to alter or process different sections of the material. Furthermore, even in homogeneous materials, different sections within a processing procedure may require different energy levels. [0005]In light of the above, it is an object of the present invention to provide a system and a method for predetermining the energy level required to alter or process a section of material, and then using the corresponding maximum pulse repetition rate with a view toward reducing the time required to perform a material processing procedure. Another object of the present invention is to provide a system and method for processing a material that effectively employs a variable pulse repetition rate to minimize the time required to perform a material processing procedure. Still another object of the present invention is to provide a system and a method for processing a material that selectively varies the pulse repetition rate of a laser beam, either pursuant to pre-programmed instructions or in response to closed loop feedback controls. Yet another object of the present invention is to provide a system and a method for processing a material that is relatively simple to manufacture, is easy to use, and is comparatively cost effective. SUMMARY OF THE INVENTION [0006]In accordance with the present invention, a system for processing materials includes a laser source for generating a laser beam. Specifically, the beam includes a sequence of laser pulses that each have a predetermined energy level. Further, the duration of each pulse in the laser beam is ultra short, and is preferably in the range of picoseconds or femtoseconds. With this in mind, it is an important aspect of the present invention that the laser source be operated to vary the repetition rate of laser pulses in the beam. [0007]In addition to the laser source, the system of the present invention also includes optics for directing the laser beam to a target area (e.g. focal spot) and to then move the interaction point along a path through the material that is to be processed. As implied above, the system also includes an evaluator that determines a required (i.e. predetermined) energy level for each laser pulse at particular focal spots. Specifically, the value of this required energy level is whatever is necessary to process the material at the focal spot (e.g. target area). [0008]A control unit is also provided for identifying a required pulse repetition rate, based on the predetermined required energy level mentioned above. Further, a selector is provided for varying the required pulse repetition rate, as necessary, in order to establish and maintain the required energy level in the laser pulses. As envisioned for the present invention, variations in the pulse repetition rate of the laser beam can be automatically made by the selector during a procedure. For this purpose, the selector can respond to either pre-programmed instructions, or to closed loop feedback controls. [0009]As an example of a procedure that can be usefully performed by the system of the present invention, consider a substantially transparent material that may have different energy level processing requirements (e.g. different energy thresholds) within the material. In such a case it may well be advantageous to vary the pulse repetition rate with a view toward minimizing the time required to perform the procedure. For instance, this can be done by using a first required pulse repetition rate (R.sub.1) on a processing section having a relatively high energy processing requirement (P.sub.1), and using a second required pulse repetition rate (R.sub.2) on a processing section having a relatively low energy processing requirement (P.sub.2). In the procedure, R.sub.1 is not equal to R.sub.2, instead R.sub.2 will be faster (e.g. R.sub.1<R.sub.2). [0010]For the present invention, it is envisioned that the processing (i.e. ablation) of materials will involve altering the material during a laser-material interaction. As noted above, this interaction can be a laser induced optical breakdown (LIOB), photodecomposition, or photoablation. In any event, it is also envisioned that this laser-material interaction will induce an identifiable response from the material. For example, the identifiable response from LIOB may be a gas bubble, and the identifiable response from photoablation may be a plasma spark. For the embodiment of the present invention that relies on closed loop feedback control, the identifiable response from the laser-material interaction is monitored by a detector. A switch that is connected to the selector can then be operated in response to signals from the detector. Specifically, the switch/selector combination for this embodiment of the present invention will then change the pulse repetition rate of the laser beam, as appropriate. Effectively, all of this is done as a feedback control in response to changes in the identifiable response in the material. BRIEF DESCRIPTION OF THE DRAWINGS [0011]The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: [0012]FIG. 1 is a graph showing the relation between pulse energy and repetition rate in a typical ultra short pulse laser source; [0013]FIG. 2 is a schematic of a system for processing a material in accordance with the present invention; [0014]FIG. 3A is a representation of a beam path through a non-homogeneous (e.g. composite) material as envisioned for the present invention; [0015]FIG. 3B is a representation of a beam path through a homogeneous material, wherein different sections of the material have different processing requirements; and [0016]FIG. 4 is a representative view of a cross section of an eye showing a procedure using the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS [0017]Referring initially to FIG. 2, a system for processing a material in accordance with the present invention is schematically shown and is generally designated 10. As shown, the system 10 includes a laser source 12 and a selector 14. The laser source 12 is also connected to a beam delivery optics 16. These various components of the system 10 (i.e. laser source 12, selector 14 and beam delivery optics 16) are each also connected in two-way electronic communication with a control unit 18. Further, the system 10 also includes a switch 20 that is interconnected between the control unit 18 and the selector 14. As disclosed below, the switch 20 is optional and may be selectively used in the operation of the system 10, if desired. Additionally, the system 10 can include an energy/controller (attenuator) 21. Specifically, the energy/controller 21 can be installed for fine adjustments of the energy in pulses of pulsed laser beam 22 that are generated by the laser source 12. Preferably, the pulse energy/controller 21 is of a type disclosed in U.S. patent application Ser. No. 10/835,088 which is assigned to the same assignee as the present invention. [0018]Still referring to FIG. 2, it is to be appreciated that the system 10 is intended to generate a pulsed laser beam 22, and to direct the laser beam 22 to a target material 24 (i.e. workpiece) for the purpose of processing the material 24. As envisioned for the present invention, the pulsed laser beam 22 will comprise a sequence of laser pulses, wherein each pulse has an ultra short duration (e.g. picoseconds or femtoseconds duration), and it will have a pulse repetition rate that can be varied. As also envisioned by the present invention, the pulsed laser beam 22 will interact with the target material 24 to cause a laser-material interaction (e.g. an ablation such as laser induced optical breakdown (LIOB), photo decomposition or photoablation). Further, a consequence of the laser-material interaction (i.e. ablation) will be the creation of an identifiable response from the target material 24. Typically, such a response is produced as the laser beam 22 processes or alters the target material 24. For example, in the case of LIOB, this identifiable response may be the size of a gas bubble. In the case of photoablation, the identifiable response may be a plasma spark. In all cases it is envisioned that the target material 24 will somehow be altered (e.g. cut, shaped, destroyed or removed) by the laser-material interaction. Depending on the type material being processed, and the nature of the desired change in the material, the laser-material interaction may either be superficial or intra-material. [0019]FIG. 2 also shows that the system 10 includes a detector 26 that, if used, will monitor the identifiable response that results from a laser-material interaction. For this purpose, the detector 26 is electronically connected to the control unit 18 to relay information to the control unit 18 about the existence or change in an identifiable response. Also, an evaluator (user interface) 28 is provided to give input to the control unit 18. Specifically, as envisioned for the system 10, the evaluator 28 can be any means known in the pertinent art that will provide the control unit 18 with information about the laser pulse energy levels that are required for an effective laser-material interface with the target material 24. Continue reading... Full patent description for Material processing system with variable repetition rate laser Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Material processing system with variable repetition rate laser patent application. Patent Applications in related categories: 20080205458 - Laser beam irradiation apparatus and laser beam machining apparatus - A laser beam irradiation apparatus including: a laser beam oscillation unit having a pulsed laser beam oscillator for oscillating a pulsed laser beam, and a repetition frequency setter; an acousto-optical deflector by which the pulsed laser beam oscillated by the laser beam oscillation unit is deflected and the output is ... ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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